After repeated U.S. bans on imports of food from China over the years, China returned the favor by banning, for the first time, imports of certain shellfish from Washington state, Oregon, Alaska and Northern California over high levels of arsenic and a toxin that causes paralytic shellfish poisoning (PSP).

The ban applies to clams, oysters and other two-shelled bivalves, according to Seattle radio station KUOW, which broke the story. It will take a particular toll on Washington’s Puget Sound, where 5 million pounds of giant geoduck (pronounced “gooey-duck”) clams are harvested annually.

The U.S. exported $68 million worth of geoduck clams in 2012, and 90% of them went to China. The Northwest exports about $270 million a year worth of shellfish annually. The clams are not a fan favorite in the United States outside of Chinese cuisine. But in China, they retail for between $100 and $150 a pound.

China issued the ban a week ago after government inspectors said they found unacceptable levels of toxins. Details are still hazy, but the U.S. believes the shellfish came from Washington or Alaska. Officials at the National Oceanic and Atmospheric Administration scrambled over the weekend to arrange meetings with their Chinese counterparts to ascertain the extent of the problem and consider possible solutions.

Health departments in the states routinely test for PSP, a biotoxin produced by the algae that shellfish eat. It can cause illness and death in humans at high levels. Recent testing in Washington found PSP levels far below international standards, according to the Seattle Times.

“We’ve gone back and looked at all records—they show results way below any human-health concern,” Donn Moyer, a health-department spokesman, told the newspaper. “We don’t have any evidence or information whatsoever about any high levels of PSP in any shellfish.”

The effect of the ban on California is unknown. It does not extend to Southern California. But the impact is being felt immediately to the north, where fishermen have been working feverishly to harvest the shellfish in the runup to the Asian New Year at the end of January. Geoduck clams can weigh up to 15 pounds and live up to 160 years. They are found from the intertidal zone to water more than 300 feet deep.

China and the U.S. have wrangled for years over food imports and exports. The Chinese have banned U.S. beef since 2003 over fears of mad cow disease, and the U.S. has taken a hard line on Chinese poultry, which was most recently linked to the death of 500 pet dogs here from eating suspect jerky products.

Both countries are continually involved in serious international trade disputes over the safety of their products, organic and manufactured. The U.S. lets agribusiness use chemicals and genetically-modified food products that other countries disapprove of and China’s exports include harmful toys and building materials.

U.S. imports from China are about four times its exports, according to the U.S. Census Bureau. They were about even in 1985. The U.S. ran a $6 million trade imbalance. It’s trade imbalance so far this year is $267 billion. Fish and shellfish combined were the 27th largest export to China in 2012, behind “computer accessories” and ahead of “pharmaceutical preparations.”